1. Field of the Invention
The present invention relates to a network facsimile communication control method which controls a network facsimile communication system including Internet fax devices and a server, the Internet fax devices having both a capability of exchanging fax images over a public switched telephone network and a capability of exchanging messages over the Internet, the server having a file transfer capability and being provided on the Internet.
2. Description of the Related Art
Recently, a network facsimile communication system using Internet fax devices is becoming practical. The Internet fax devices have both a capability of exchanging fax images over the public switched telephone network (PSTN) and a capability of exchanging messages over the Internet.
ITU-T recommendations T.37 and T.38 are provided for the standards of store-and-forward fax via an electronic mail (e-mail). ITU-T recommendation T.37 defines store-and-forward fax via e-mail through the incorporation of specified communication protocol. Fax image documents are attached to e-mail headers and are encoded in the specified data format. ITU-T recommendation T.38 addresses IP fax transmissions for IP-enabled fax devices and fax gateways, defining the translation of T.30 fax signals and Internet fax protocol packets.
With the above-mentioned ITU-T recommendations, the Internet fax devices which are provided with both the capability of exchanging fax images over the PSTN and the capability of exchanging messages over the Internet are put into practical use.
In addition, there have been some approaches for exchanging fax images over the Internet by using e-mail, which are described in the RFC (request for comments) 2301 through 2306 published by the IETF (Internet Engineering Task Force).
The e-mail transmission protocols are shared by the T.37 and the RFC 2305 (simple mode fax). This makes it possible to exchange fax images via e-mail between the Internet fax devices which conform to the T.37 and the workstations or network facsimile devices which incorporate application programs conforming to the RFC 2305.
However, there is a case in which a call to the PTSN is initiated by one Internet fax device of the network facsimile communication system, and the called number, keyed in the calling Internet fax device, indicates a fax number of another Internet fax device on the PSTN. In the existing facsimile communication system, the call setup is established with respect to the PSTN in this case, and the fax transmission and reception is performed between the calling and called Internet fax devices via the PSTN. Although the Internet fax devices have the capability of exchanging messages over the Internet, the PSTN-based fax transmission and reception is performed in this case. In view of the transmission speed and transmission capacity, it is conceivable that the cost of the PSTN-based communications is higher than the cost of the Internet-based communications. Accordingly, in order to reduce the cost of communications of the Internet fax devices, it is desired to provide a communication control method that carries out the fax communications of the Internet fax devices over the Internet, rather than over the PSTN, when a call to the PSTN is initiated by one of the Internet fax devices.